The metabolism of arachidonic acid to the physiologically active agents, prostaglandins, thromboxanes, prostacyclin, and malonaldehyde occurs in two stages. The first stage involves the oxygenation of arachidonate to the hydroperoxy endoperoxide, PGG2, and its subsequent reduction to the hydroxy endoperoxide, PGH2. These sequential reactions occur in virtually all mammalian tissues. In the second stage, PGH2 is metabolized to one of the above named agents in a tissue specific fashion. We have discovered that during the reduction of PGG2 to PGH2 an oxidizing agent is produced which is capable of oxidizing tissue components, drugs, and chemical carcinogens. The oxidation can occur by either dehydrogenation or by oxygenation of the cosubstrate. We have concentrated our initial studies on the oxygenative metabolism of xenobiotics since oxidative metabolism has been found to be important in the toxicity and carcinogenicity of many environmental agents. We have shown that the PGG2 dependent oxidation of diphenyl isobenzofuran and phenylbutazone by enzyme preparations from ram seminal vesicles proceeds by a free radical mechanism and results in the incorporation of one atom of oxygen from oxygen gas into the carbon framework. We propose to determine the identity of the oxidizing agent produced by the interaction of PGG2 with the vesicular gland peroxidase. Experiments are described which will determine whether the oxidizing agent is hydroperoxidase or enzyme derived. We also propose to determine the extent of xenobiotic oxidation by arachidonic acid and by NADPH dependent pathways in tissues of the mouse and rat. This will enable us to evaluate the possibility that prostaglandin synthetase acts as an alternate enzyme system to the mixed-function oxidases for the oxidative metabolism of foreign compounds in vivo.